Systems and methods for flow sensor back pressure adjustment for mass flow controller

ABSTRACT

A mass flow control apparatus comprising a proportional valve upstream of a flow measurement portion, a pressure sensing element fluidly connected to determine a fluid pressure downstream of the flow measurement portion, and a dynamically adjustable variable valve downstream of the flow measurement portion and adjacent to the pressure sensing element connection. Fluid conductance of the variable valve is adjusted according to a control scheme based upon limitations of the flow measurement portion. Integral flow verification may be enabled with additional fluid pathway elements upstream of the flow measurement portion.

PRIORITY CLAIM TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/907,254, filed Feb. 27, 2018, entitled as “SYSTEMS AND METHODS FORFLOW SENSOR BACK PRESSURE ADJUSTMENT FOR MASS FLOW CONTROLLER”, whichclaimed the benefit of U.S. Provisional Patent Application No.62/464,251, filed Feb. 27, 2017, entitled as “Systems, Apparatus andMethods for Flow Sensor Back Pressure Adjustment for Mass Flow Control”,the disclosures of which are incorporated by reference in theirentirety.

BACKGROUND

Various embodiments relate to mass flow control apparatus. Mass flowcontroller may operate by modulating a fluid pressure. Fluid as usedherein is intended to encompass materials which are in a gaseous phasebecause of specific combinations of pressure and temperature despitewhether such materials are gaseous under everyday circumstances. Thus,fluids may include water vapor or boron trichloride (BCl3), for example,along with common gaseous materials such as silane (SiH4), argon,nitrogen, etc. The embodiments described below relate to determining thepresent flow conditions at a flow restriction in a fluid flow pathway toascertain whether or not a chosen flow control algorithm is valid forthose present conditions. At various times, a low fluid flow rate may berequired while a silicon manufacturing chamber may also provide backpressure. Providing a low fluid flow rate in a backpressure environmentmay be challenging. Various embodiments described below are directed toaddressing issues related to low flow conditions with back pressure fromthe upstream direction.

SUMMARY

In consideration of the foregoing applicant has invented a fluid massflow control apparatus comprising three valves, a flow restriction, andprovisions for determining three different fluid pressures and at leastone temperature.

In accordance with one embodiment, a mass flow control apparatus isprovided that includes a control module configured to receive a firstset point for delivering a fluid delivery to a tool, responsive to thecontrol module receiving a second set point that is significantly lowerthan a first set point, a variable control valve located downstream fromthe flow restrictor and downstream from a first pressure sensorconfigured to constrict to reduce the flow of the fluid responsive toreceiving the second set point. The mass flow controller apparatusfurther including solenoid type valve as a variable control valve. Thevariable control valve is configured to control the downstream pressurefrom the flow restrictor. A second pressure sensor located upstream fromthe variable control valve, the second pressure sensor configured tomeasure back pressure from the tool. The variable control valveconstricts sufficiently to increase the pressure of the fluid from theflow restrictor to be higher than the measured back pressure from thetool and adjust the pressure to the flow restrictor such that thepressure drops across the flow restrictor to yield a flow rate that isequal to the second set point. A proportional control valve that is asolenoid valve to control the pressure to the flow restrictor and ashutoff valve including a solenoid valve to close the inlet supply toperform a rate of decay measurement operation.

In another embodiment, a mass flow control apparatus is provided thatincludes a proportional valve upstream of a flow measurement portion, apressure sensing element fluidly connected to determine a fluidpressure, downstream of the flow measurement portion and a dynamicallyadjustable variable valve downstream of both the flow measurementportion and the pressure sensing element connection. A solenoid valve tocontrol pressure to a flow restrictor with a proportional control valvethat is a solenoid valve to control the pressure to the flow restrictor.A shutoff valve comprises a solenoid valve to close the inlet supply toperform a rate of decay measurement operation. A pressure-based flowsensor including a fluid conduit with fluidly coupled pressure andtemperature sensing provisions upstream of a known flow restriction. Athermal-based flow sensor includes fluid conduit with two spaced aparttemperature responsive elements affixed to the exterior of the fluidconduit. The dynamically adjustable variable valve can be adjusted toany of at least two different amounts of openings. The dynamicallyadjustable variable valve can be continuously adjusted to a range ofopenings.

In various embodiments, a mass flow control apparatus is provided thatincludes an inlet to a fluid pathway, a controllable shutoff valve, thecontrollable shutoff valve providing provisions for measuring areference temperature (T0) and a reference pressure (P0) of a fluidcontained within a reference volume of the fluid pathway, a proportionalcontrol valve, the proportional control valve providing provisions formeasuring a first temperature (T1) and a first pressure (P1) of thefluid contained within the fluid pathway upstream of a flow restriction,the flow restriction providing provision for measuring a second pressure(P2) of the fluid contained within the fluid pathway downstream of theflow restriction, a variable valve and an outlet from the fluid pathway.The flow restriction is chosen from group of an orifice, a nozzle, aporous sintered metal element or a laminar flow structures. Asupervision function may choose an action from group of self-calibrationprocess, change of system parameter or storage of results.

In various embodiments, a method for a mass flow control apparatus isprovided, including determining a fluid pressure downstream of a flowsensor, responding to the fluid pressure downstream and adjustingdynamically a variable valve downstream of the flow sensor to maintaindesired operating conditions in the flow sensor; and maintaining andextending the useful operating range of the mass flow control apparatus.The method further including a flow verification capability. The flowverification capability including the steps of closing a shutoff valveto isolate a fluid pathway from an inlet while controlled mass flowcontinues through an outlet; making repeated measurements of a referencevolume of a fluid pathway for a period of time, opening the shutoffvalve to re-establish fluid pathway connection to the inlet, calculatinga verified flow signal using pressure-volume-temperature methods; andproviding a verified flow signal to a supervision function. Thesupervision function directs that a series of flow verificationmeasurements be performed corresponding to different values ofdetermined fluid pressures and fluid temperatures adjacent the flowrestriction and determines a calibration curve for a discrete flowrestriction based on the flow signals generated by the flow verificationmeasurements.

A mass flow control apparatus including a control module configured toreceive a first set point flow rate for delivering a fluid delivery to atool, responsive to the control module receiving a second set point thatis significantly lower that a first set point flow rate: a variablecontrol valve located downstream from a flow restrictor and downstreamfrom a first pressure sensor, the variable control valve configured toconstrict to adjust the pressure of the fluid responsive to receivingthe second set point flow rate; and a proportional control valve locatedupstream from the flow restrictor to adjust the pressure to the flowrestrictor. In some embodiments the variable control valve is a solenoidtype valve. In various embodiments, the proportional control valve is asolenoid type valve. In various embodiments, the variable control valveis configured to control the pressure downstream from the flowrestrictor responsive to receiving a significantly lower second setpoint; and wherein significantly lower is 5% of full scale fluid flowrate. In some embodiments, significantly lower would be at least one of60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% of the previously request setpoint flow rate.

In various embodiments, the variable control valve constricts the fluidflow the flow path sufficiently to increase the pressure of the fluidfrom the flow restrictor to be higher than a back pressure from the tooland the proportional control valve is configured to adjust the pressureto the flow restrictor such that the pressure drop across the flowrestrictor yields a flow rate that is equal to the second set point. Invarious embodiments, a reference volume may be configured to verify theactual flow rate by closing the fluid flow using a shut off valve andmeasuring the pressure rate of decay in the reference volume andadjusting one or both of the variable control valve or the proportionalcontrol valve until the second set point flow rate is achieved. In someembodiments, the mass flow controller may use thermal-based flow sensorand a supervision function. The mass flow control may include athermal-based flow sensor with a fluid conduit with two spaced aparttemperature responsive elements affixed to the exterior of the fluidconduit. In some embodiments, a variable control valve can be adjustedto any of at least two different amounts of openings. In someembodiments, a variable control valve can be continuously adjusted to arange of openings. In some embodiments, a the variable control valve canbe adjusted to a provide a complete shut-off position. In someembodiments, a shut-off valve upstream from a reference volume, whereinthe reference volume is upstream from a flow restrictor, the shut-offvalve configured to close the inlet supply to perform a rate of decayoperation; and wherein the shut-off valve is a solenoid type valve. Insome embodiments, a first pressure sensor is configured to measure fluidpressure (P0) and a first temperature sensor is configured to measuretemperature (T0) of a reference volume downstream from the shutoffvalve; a proportional control valve, the proportional control valveproviding provisions for measuring a second temperature (T1) and asecond pressure (P1) of the fluid contained within the fluid pathwayupstream of a flow restriction; the flow restriction providing provisionfor measuring a third pressure (P2) of the fluid contained within thefluid pathway downstream of the flow restriction; and an outlet from thefluid pathway. In some embodiments, a shut-off valve upstream from areference volume, the reference volume is upstream from a flowrestrictor, the shut-off valve configured to close the inlet supply toperform a rate of decay operation; wherein the shut-off valve is asolenoid type valve, and a proportional control valve that is a solenoidvalve to control the pressure to the flow restrictor. In someembodiments, the flow restrictor is chosen from group comprising of anorifice, a nozzle, a porous sintered metal element, a laminar flowstructures or tubes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic of a pressure-based flow controller.

FIG. 1B is a schematic of a thermal-based flow controller.

FIG. 2A is a schematic of a mass flow controller with a proportionalvalve upstream of a flow measurement portion.

FIG. 2B is a schematic of a mass flow controller with a proportionalvalve downstream of a flow measurement portion.

FIG. 2C is a schematic of a mass flow controller that is capable ofpressure monitoring downstream of a flow measurement portion.

FIG. 3 is a schematic of a mass flow controller that includes a pressuresensing element connection downstream of a flow measurement portion anda dynamically adjustable variable valve further downstream of thepressure sensing element.

FIG. 4 is a schematic of a mass flow controller that includes a flowverification capability while using a pressure-based flow sensor.

FIG. 5 is a schematic of a mass flow controller that includes adynamically variable valve downstream of a flow Measurement portion anda pressure sensing element connection further downstream of the variablevalve.

FIG. 6 is a schematic of a mass flow controller that includes a flowverification capability while using a pressure-based flow sensor.

FIG. 7 is an illustration showing portions of a complex fluid deliverysystem within a single large apparatus for processing semiconductordevices.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phrasing and terminology used herein isfor the purpose of description and should not be regarded as limiting.The use of “including,” “comprising,” or “having,” “containing,”“involving,” and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems. The use of directional adjectives “inner, outer,” “upper,”“lower,” “upstream”, “downstream” and like terms, are meant to assistwith understanding relative relationships among design elements andshould not be construed as meaning an absolute direction in space norregarded as limiting.

Embodiments are directed to systems and methods for a mass flowcontroller for responding to a request for a large reduction in flowrate or a large step down in flow rate. For example, a semiconductormanufacturing recipe may require a drop from 500 cc flow rate to drop to25 cc. The bleed down time or the amount of time a mass flow controlstakes to provide the reduction should be fast. Embodiments are directedto providing a variable control valve located downstream from each ofthe following elements within a mass flow controller: fluid statesensing element (including reference volume, pressure sensor andtemperature sensor), proportional valve, additional pressure andtemperature sensors, flow restrictor and third pressure sensor. As willbe discussed in greater detail below the variable control valve may beused to achieve faster step down response times. In some embodiments,the third pressure sensor may be located downstream from the variablevalve and upstream from the fluid outlet. In various embodiments, uponreceiving a signal to reduce the flow rate by 80%, 85%, 90% or 95%(greater than 80% or 90%) from the previous flow rate, the variablecontrol value may be constricted thus increasing the pressure at thepressure sensor located closest to the variable control valve.Additionally, when the variable control valve is shutoff the inletpressure may be increased and the pressure at other pressure sensors mayshow an increase.

As described herein, by constricting the variable control valve the massflow controller may be able to change its flow rate significantly whilebeing able to conduct a rate of decay calculation. In some embodiments,the variable control valve may be a solenoid valve to control pressureto the flow restrictor (laminar flow element, orifice, hagen pouiselletube) that may reduce cost of manufacturing. The variable valve that maybe solenoid valve may act as a shutoff valve to perform a rate of decayoperation to determine the flow rate. In various embodiments, thevariable control valve may be a proportional control valve that is asolenoid to control the pressure to the flow restrictor and locatedupstream of the flow restrictor. The solenoid type proportional controlvalve may be used to close the inlet supply to perform a rate of decayoperation.

FIG. 1A is a schematic of a pressure-based flow controller. Arepresentative example of a pressure-based flow controller 100 (FIG. 1A)includes fluid inlet 102, a fluid conduit 104 (e.g., a bore in a largerbody of material or the like), a pressure sensor 106, a temperaturesensor 108, a flower restrictor 110, a control module 112, a flow signal(e.g., set point or flow rate indicator), a fluid outlet 116.

The fluid conduit 104 may be fluidly coupled to the pressure sensor 106and temperature sensor 108 upstream of a known flow restrictor 110. Thepressure sensor 106 and temperature sensor 108 may be individualelements or function as a combined single unit element. The controlmodule 112 may receive signal from and send signals to the temperatureand pressure sensors (106 and 108). The control module 112 may controlthe flow restrictor 110 to achieve desired flow rate by adjusting thepressure and/or temperature to achieve a flow rate. The control module112 may determine corresponding pressure and temperature conditions fora fluid moving through the conduit 104 whereby the mass flow rate may becalculated based upon characteristics of the known flow restrictionprovided by the flow restrictor 110. The known flow restrictor 110 maybe an orifice, nozzle, porous sintered metal element, or even a laminarflow structure such as a plurality of long narrow flow passageways.Knowledge of the pressure-temperature-flow characteristics of the flowrestriction is often obtained by measurements made during a flowcalibration process but other methods, such as direct measurement ofmechanical dimensions, may also be feasible in some designs.

The control module 112 may include circuitry to control the variouselements shown in FIG. 1A. The control module 112 may generate a flowrate signal 114 and provide excitation, sense, measure and calculatebased on the received signals. In some embodiments, the control module112 may receive a pressure measurement from the pressure sensor 106 andreceive a temperature from the temperature sensor 108. The controlmodule 112 may adjust the flow restrictor 110 based on the desired setpoint received from an external system. The control module 112 may beconfigured to use the measured pressure to determine the actual flowrate based on historical calibration information for the system 100. Thepressure sensor 106 may generate a pressure P1 and generate a signalthat represents a pressure to the control module 112 that controls theflow restrictor 110. The temperature sensor 108 may generate atemperature T1 and generate a signal to the control module 112 thatrepresents a temperature T1 to the control module 150. Next thegas/fluid may pass through a flow restrictor 110 to the outlet 116.

FIG. 1B is a schematic of a thermal-based flow controller 150. Arepresentative example of a thermal-based flow sensor (FIG. 1B) includesa fluid inlet valve 152, a fluid conduit 154 (typically a capillarytube) with two spaced apart temperature responsive elements 156 and 158(herein illustrated as resistance windings) affixed to the exterior ofthe fluid conduit. Electronic circuitry in the control module 154provides excitation to the temperature responsive elements and senseschosen properties of the elements whereby heat transfer caused by afluid moving through the conduit 154 may be measured and a correspondingmass flow calculated. A typical mass flow meter may additionally includea known laminar flow element (not shown) fluidly coupled in parallelwith the thermal-based flow sensor whereby a proportionate fluid flowpasses through the laminar flow element. The control module 164 maygenerate a flow signal 162 that is indicative of the flow rate of thefluid through the fluid conduit 154.

FIG. 2A is a schematic of a mass flow controller 200 that includes afluid inlet 202 at pressure P0, a fluid conduit 204, a proportionalvalve 206, a flow measurement module 208, a flow control 210, a fluidoutlet 212, and a flow set point 214. The proportional valve 206 may belocated upstream of a flow measurement module 208. A representative massflow controller 200 (MFC) may include a flow measurement module 208 anda proportional valve 206 upstream (FIG. 2A) of the flow measurementmodule 208, the upstream valve being actively modulated by a flowcontrol module 210 (typically electronic circuitry) to adjust the fluidflow to match a desired flow set point.

Referring to FIG. 2B, FIG. 2B illustrates a mass flow controller 220that includes a fluid inlet 222, a fluid conduit 224, a flow measurementmodule 226, a proportional valve 228, a valve command 230, a flowcontroller 232 and a flow set point 234. The flow measurement module 226may include a pressure sensor, a temperature sensor. The mass flowcontroller 220 may include a proportional valve 228 downstream (FIG. 2B)of the flow measurement module 210, the downstream valve 228 beingactively modulated by a flow control module 232 (typically electroniccircuitry) to adjust the fluid flow to match a desired flow set point234. The mass flow controller 220 arrangement with an upstreamproportional valve 228 (FIG. 2A) advantageously provides the flowmeasurement portion some isolation from deleterious effects of pressuretransients at the fluid inlet 222. In case of a thermal-based flowsensor (FIG. 1B), the upstream proportional valve MFC arrangement (FIG.2A) may directly subject the flow sensor to very low fluid outletpressures which may adversely change to nonlinear heat transfer causedby fluid moving through the conduit. The MFC arrangement with adownstream proportional valve 228 (FIG. 2B) advantageously provides theflow measurement portion 226 some isolation from deleterious effects oflow pressure and/or pressure transients at the fluid outlet 228.However, such arrangement directly exposes the flow measurement portion226 to the deleterious effects of pressure transients at the fluid inlet222. In case of a pressure-based flow sensor (e.g. FIG. 1A), thedownstream proportional valve arrangement (FIG. 2B) possibly makes thepressure drop across the flow restriction sub-critical. The pressure atthe downstream side of the flow measurement portion 248 may be monitored(FIG. 2C) to determine whether a thermal-based flow measurement portionis operating in nonlinear conditions or whether a pressure-based flowmeasurement portion is operating in sub-critical conditions.

FIG. 2C is a schematic of a mass flow controller 240 that is capable ofpressure monitoring downstream of a flow measurement portion. The massflow controller 240 includes a fluid inlet 242, a fluid conduit 244, aproportional valve 246, a flow measurement 248, a pressure sensor 250, aflow control module 252, a valve command 254, a flow set point 256 and afluid outlet 258. The pressure at the downstream side of the flowmeasurement portion 248 may be monitored (FIG. 2C) to determine whethera thermal-based flow measurement portion is operating in nonlinearconditions or whether a pressure-based flow measurement portion 248 isoperating in sub-critical conditions. The flow control module 252 may beconfigured to receive a flow set point 256 and send commands to theproportional valve 246. Pressure sensor 250 generates a pressure signal251 as an input to flow control 252. The flow control 252 receives thepressure signal 251 and determines the flow rate and may adjust theproportional valve 246.

FIG. 3 is a schematic of a mass flow controller 300 that includes afluid inlet 302, fluid conduit 304, a proportional valve 306, a flowmeasurement module 308, a pressure sensor 310, a variable valve 313, arange decision module 314, a flow control 316, a flow set point 320 anda fluid outlet 322. Mass flow controller 300 includes a pressure sensor310 downstream of a flow measurement module 314 and a dynamicallyadjustable variable valve 312 further downstream of the pressure sensor310. An embodiment of the mass flow control controller 300 (FIG. 3)includes a proportional valve 306 upstream of a flow measurement module308, a pressure sensor 310 fluidly connected to determine a fluidpressure downstream of the flow measurement module 308, and adynamically adjustable variable valve 312 downstream of both the flowmeasurement module 308 and the pressure sensor 310. The downstreampressure sensor 310 and variable valve 312 may be used with either apressure-based or a thermal-based flow sensor. The variable valve 312may be controllably adjusted (set) to any of at least two differentamounts of opening (fluid conductance).

The variable valve 312 may additionally provide a complete shut-off in athird adjustment condition (setting) although this capability isoptional. The variable valve 312 may be of a type with a continuouslyadjustable range of openings. The pressure sensor 310 may be of anyconvenient type and may optionally further include fluid temperaturemeasuring provisions such as a temperature sensor.

An adjustment decision may be made, and opening of the variable valve312 consequently adjusted, in response to a magnitude of the determinedfluid pressure downstream of the flow measurement module 308 relative toa chosen threshold. The chosen threshold may be selected to ensure theflow measurement module 308 is subjected to at least a minimum (one halfatmosphere, for example) determined downstream fluid pressure.Alternatively, in some embodiments, the chosen threshold may be selectedto ensure the flow measurement portion is operating in a desired linearregime. The opening of the variable valve 310 may be held relativelyconstant, and specifically changed according to known limitations of theflow measurement module 308, with intentional hysteresis caused byselecting a new chosen threshold contemporaneous with each specificchange of opening. Yet another control scheme may dynamically modulatethe adjustment of the variable valve 312 to maintain a relativelyconstant determined fluid pressure downstream of the flow measurementmodule 308. In yet another embodiment, the flow controller 316 may use acontrol scheme to select the chosen threshold based at least in partupon the pressure drop across the flow measurement module 308. Inanother embodiment, the flow controller 316 may use a control method toselect the chosen threshold based at least in part on the change ofpressure across the flow measurement module 308. The proportional valve306 and the variable valve 312 control the flow of the fluid through themass flow controller 300. The variable valve 312 may be used to help themass flow controller 300 have a faster step-down response when reducingthe flow by more than 50%. In other embodiments, the variable valve 312may be used to help the mass flow controller 300 have a faster step upresponse when increasing the flow of the fluid by more than 50%.

FIG. 4 is a schematic of a mass flow controller 400 that includes a flowverification capability while using a pressure-based flow sensor. Themass flow controller 400 may comprise (in upstream to downstream flowsequence) a fluid inlet 402, to a fluid pathway 404, a controllableshutoff valve 406, provisions for measuring a reference temperature 412(T0) and a reference pressure 410 (P0) of a fluid contained within areference volume 408 of the fluid conduit 404, a proportional controlvalve 414, provisions for measuring a first temperature 418 (T1) and afirst pressure 416 (P1) of the fluid contained within the fluid pathwayupstream of a flow restriction 420, provisions for measuring a secondpressure 422 (P2) of the fluid contained within the fluid pathwaydownstream of the flow restriction 420, a variable valve 424, and anoutlet 426 from the fluid pathway 404. Knowing the aggregate volume offluid contained within the reference volume 408, plus any directlyconnected fluid conduit 404 between the shutoff valve 406 and theproportional valve 414, enables flow verification (self-calibration) ofthe embodiment mass flow controller 400. Flow verification methodincludes closing the shutoff valve 406 to isolate the fluid conduit 404from the inlet 402 while controlled mass flow continues through theoutlet, making repeated measurements of the reference temperature 410(T0) and the reference pressure 412 (P0) of the fluid contained withinthe reference volume 408 of the fluid conduit 404 for a period of time,opening the shutoff valve 406 to re-establish fluid pathway connectionto the fluid inlet 402, calculating a verified flow signal usingpressure-volume-temperature (PVT, also known as Rate Of Fall, RoF)methods related to the aggregate volume of fluid, and providing theverified flow signal to a supervision function (control module 428). Thecontrol module 428 may subsequently choose whether to enable additionalself-calibration processes, change a system parameter, merely store theresults, or take other actions. For example, the control module 428 maydirect that a series of flow verification measurements be performedcorresponding to different values of determined fluid pressures (P1, P2)and fluid temperature (T1) adjacent the flow restriction 420. Thisseries of flow verification measurements readily determines acalibration curve, for a discrete flow restriction, based at least inpail upon the verified flow signals. It should be noted the controlmodule 428 does not require any particular critical ratio (P1/P2) bemaintained between the determined upstream (P1) and downstream (P2)pressures when a known calibration curve is obtained. The knowncalibration curve may be entirely empirical or conform to a theoreticalmodel.

FIG. 5 is a schematic of a mass flow controller 500 that includes adynamically variable valve downstream of a flow measurement module 508and a pressure sensing element 512 further downstream of the variablevalve 510. Another embodiment of a mass flow controller 500 (FIG. 5)includes a proportional valve 506 upstream of a flow measurement portion508, a dynamically adjustable variable valve 510 downstream of the flowmeasurement portion, and a pressure sensing element fluidly connected todetermine a fluid pressure downstream of the flow measurement portionand the adjustable variable valve. The downstream pressure sensingelement 512 and variable valve 510 combination may be used with either apressure-based or a thermal-based flow sensor. The variable valve 510may be controllably adjusted (set) to any of at least two differentamounts of opening (fluid conductance). The variable valve 510 mayadditionally provide complete shut-off in a third adjustment condition(setting) although this capability is optional. The variable valve 510may be of a type with a continuously adjustable range of openings. Thepressure sensing element 512 may be of any convenient type and mayoptionally further include fluid temperature measuring provisions. Anadjustment decision may be made by the range decision 516, and openingof the variable valve 510 consequently adjusted, in response tooperating conditions of the apparatus as further explained below.

FIG. 6 is a schematic of a mass flow controller 600 that includes a flowverification capability while using a pressure-based flow sensor. Invarious embodiments, of a mass flow controller 600 may additionallyinclude a flow verification capability (FIG. 6). The mass flowcontroller 600 includes (in upstream to downstream flow sequence) aninlet 602, a fluid pathway 604, a controllable shutoff valve 606,provisions for measuring a reference temperature 612 (T0) and areference pressure 610 (P0) of a fluid contained within a referencevolume portion 608 of the fluid pathway 604, a proportional controlvalve 614, provisions for measuring a first temperature 618 (T1) and afirst pressure 616 (P1) of the fluid contained within the fluid pathwayupstream of a flow restriction 620, the flow restriction 620, a variablevalve 622, provisions for measuring a second pressure (second pressuresensor 624) (P2). In various embodiments the second pressure sensor 624may measure the fluid contained within the fluid pathway 604 downstreamof the flow restriction 620 and the variable valve 622, and an outletfrom the fluid pathway 604. Knowing the aggregate volume of fluidcontained within the reference volume 608, plus any directly connectedfluid pathway portions between the shutoff valve 606 and theproportional valve 614, enables flow verification (self-calibration) ofanother embodiment of the mass flow control apparatus. Flow verificationinvolves closing the shutoff valve 606 to isolate the fluid pathway 604from the inlet 602 while controlled mass flow continues through theoutlet 626, making repeated measurements of the reference temperature612 (T0) and the reference pressure 610 (P0) of the fluid containedwithin the reference volume 608 of the fluid pathway 604 for a period oftime, opening the shutoff valve 606 to re-establish fluid pathwayconnection to the inlet 602, calculating a verified flow signal usingpressure-volume-temperature (PVT, also known as Rate Of Fall, RoF)methods related to the aggregate volume of fluid, and providing theverified flow signal to a control module 605. The control module 605 maysubsequently choose whether to enable additional self-calibrationprocesses, change a system parameter, merely store the results, or takeother actions. For example, the control module 605 may direct that aspecific valve command be presented to the variable valve 622 and aseries of flow verification measurements performed corresponding todifferent values of determined fluid pressures (P1, P2) and fluidtemperature (T1) adjacent the flow restriction 620 and variable valve622. This series of flow verification measurements readily determines acalibration curve, for a composite flow restriction comprising theoriginal discrete flow restriction plus the partially open variablevalve 622, based at least in part upon the verified flow signals.

In various embodiments, the control module 605 may relate to making anadjustment decision using a range decision 634, and adjusting an openingof the variable valve 622 downstream of the flow measurement portion(reference volume 608), in response to a magnitude of one or moredetermined fluid pressures relative to a chosen threshold. Inparticular, if the flowing fluid pressure drop across the flowrestriction 620 and variable valve 622 (P1-P2) is less than a chosenthreshold, then a revised valve command may be presented to the variablevalve 622 causing the variable valve 622 to assume a less open more flowrestricting condition. A flow verification measurement may then providea verified flow signal for comparison with calculated mass flow (usingP1, T1, P2) through the composite flow restriction (which is comprisedof the discrete flow restriction 620 and the variable valve 622)obtained by using a previously obtained calibration curve associatedwith the particular composite flow restriction 620. If the verified flowsignal and calculated mass flow are suitably close to identical (forexample, 0.5%), then the variable valve may be considered as havingreturned to a known condition and the supervision function may affirmuse of the previously obtained calibration curve with the particularcomposite flow restriction. It should be noted the control module doesnot require any particular critical ratio (P1/P2) be maintained betweenthe determined upstream first (P1) and downstream second (P2) pressureswhen a known calibration curve has been obtained. The known calibrationcurve may be entirely empirical or conform to a theoretical model.

In low flow and low set point applications additional advantages may beobtained from a variable valve 622 that is additionally able to providecomplete shut-off in a third adjustment condition (setting). In any ofthe previously described embodiments a lower auto-shutoff threshold (forexample, 0.25% of full-scale) may be provided to the flow controlportion of a mass flow controller such that a set point request lessthan the auto-shutoff threshold causes the flow control portion toimmediately command the proportional valve to its most flow restrictingcondition without need to obtain a calculated mass flow. Similarly, avariable valve capable of shutoff may be simultaneously commanded toclose completely and thereby bring fluid flow to a very rapid halt. Inthe situation of embodiments (FIG. 3 & FIG. 4) wherein the downstreamsecond pressure (P2) is determined immediately adjacent to the discreteflow restriction, and upstream of the variable valve (described above),then a variable valve having a continuously adjustable range of openingsmay be advantageously used to control the pressure drop (P1-P2) acrossthe flow restriction while the proportional valve is commanded into itsmost flow restricting or other convenient condition.

FIG. 7 is an illustration showing portions of a complex fluid deliverysystem within a single large apparatus for processing semiconductordevices. Illustrated in FIG. 7 is an abbreviated schematic illustratingportions of a complex fluid delivery system within a single largeapparatus for processing semiconductor devices. A plurality of newembodiment mass flow controllers (of the type illustrated in FIG. 5 &FIG. 6) may be used with a plurality of process gas species to feedreactants into a plurality of vacuum chambers. Such an apparatus isoften referred to as a “tool.” As shown in the abbreviated schematic, agroup (“pallet”) of mass flow controllers (MFC.K, MFC.L) enable thesimultaneous combination of several different process gases (GAS.A,GAS.B) into a single manifold (MANIFOLD.X) which feeds a gasdistribution structure (“showerhead”-1) inside a vacuum chamber(CHAMBER.X). Insufficient conductance in some manifold plumbing (FEED.X)may result in the downstream pressure (Px2), of a particular group ofmass flow controllers, becoming too high to maintain choked flowconditions within one or more mass flow controllers within the group. Inan alternative scenario, the downstream pressure (Px2) within themanifold (MANIFOLD.X) may be so low the requisite operating conditionsinternal to a specific new embodiment mass flow controller (e.g. MFC.K)cannot be maintained as desired and the corresponding variable valvewithin the MFC adjusted as previously discussed. The pressure within themanifold may be monitored (Px2) and a corresponding signal provided toall mass flow controllers within the group (MFC.K, MFC.Q) as analternative to each mass flow controller having a separate thirdpressure sensor. Individual mass flow controller adjustment decisionsmay then proceed based upon the shared third pressure sensor signal.Each individual new embodiment mass flow controller may contain adedicated supervision function which determines a course of action or asupervision function may be associated with and shared among all newembodiment mass flow controllers comprising a specific pallet group ofMFCs.

A mass flow control apparatus comprising: a proportional valve upstreamof a flow measurement portion, a pressure sensing element fluidlyconnected to determine a fluid pressure downstream of the flowmeasurement portion and a dynamically adjustable variable valvedownstream of both the flow measurement portion and the pressure sensingelement connection. Further the mass flow control apparatus comprisingof a pressure-based flow sensor including a fluid conduit with fluidlycoupled pressure and temperature sensing provisions upstream of a knownflow restriction. Alternatively, the mass flow control apparatusincludes a thermal-based flow sensor, which has fluid conduit with twospaced apart temperature responsive elements affixed to the exterior ofthe fluid conduit. Further the dynamically adjustable variable valve canbe adjusted to any of at least two different amounts of openings, orcontinuously adjusted to a range of openings or adjusted to a provide acomplete shut-off position.

A mass flow control apparatus includes, an inlet to a fluid pathway; acontrollable shutoff valve, the controllable shutoff valve providingprovisions for measuring a reference temperature (T0) and a referencepressure (P0) of a fluid contained within a reference volume of thefluid pathway; a proportional control valve, the proportional controlvalve providing provisions for measuring a first temperature (T1) and afirst pressure (P1) of the fluid contained within the fluid pathwayupstream of a flow restriction; the flow restriction providing provisionfor measuring a second pressure (P2) of the fluid contained within thefluid pathway downstream of the flow restriction; a variable valve; andan outlet from the fluid pathway. The flow restriction is chosen fromgroup comprising of an orifice, a nozzle, a porous sintered metalelement or a laminar flow structures. Further the mass flow controlapparatus includes a supervision function. The supervision function maychoose an action from group comprising of self-calibration process,change of system parameter or storage of results.

A mass flow control apparatus including a mass flow controller furtherwhich includes a proportional valve upstream of a flow measurementportion; a dynamically adjustable variable valve downstream of the flowmeasurement portion; a pressure sensing element fluidly connected todetermine a fluid pressure downstream of the flow measurement portionand downstream of the variable valve. The mass flow control apparatusincluding the plurality of mass flow controllers; a plurality of gasspecies to feed reactants into a plurality of vacuum chambers.

A mass flow control apparatus including an inlet to a fluid pathway; acontrollable shutoff valve, the controllable shutoff valve providingprovisions for measuring a reference temperature (T0) and a referencepressure (P0) of a fluid contained within a reference volume of thefluid pathway; a proportional control valve, the proportional controlvalve providing provisions for measuring a first temperature (T1) and afirst pressure (P1) of the fluid contained within the fluid pathwayupstream of a flow restriction; the flow restriction, a variable valveproviding provision for measuring a second pressure (P2) of the fluidcontained within the fluid pathway downstream of the flow restrictionand downstream of the variable valve; and an outlet from the fluidpathway.

A method for a mass flow control apparatus including determining a fluidpressure downstream of a flow sensor; responding to the fluid pressuredownstream; and adjusting dynamically a variable valve downstream of theflow sensor to maintain desired operating conditions in the flow sensor;and maintaining and extending the useful operating range of the massflow control apparatus. The method further includes a flow verificationcapability. The method further wherein the flow verification capabilitycomprises the steps of: closing a shutoff valve to isolate a fluidpathway from an inlet while controlled mass flow continues through anoutlet; making repeated measurements of a reference volume of a fluidpathway for a period of time; opening the shutoff valve to re-establishfluid pathway connection to the inlet; calculating a verified flowsignal using pressure-volume-temperature methods; and providing averified flow signal to a supervision function. Wherein the supervisionfunction directs that a series of flow verification measurements beperformed corresponding to different values of determined fluidpressures and fluid temperatures adjacent the flow restriction. Whereinthe supervision function determines a calibration curve for a discreteflow restriction based on the flow signals generated by the flowverification measurements.

Referring to FIG. 7, FIG. 7 shows an apparatus 700 having a plurality ofself-correcting mass flow controllers may be used with a plurality ofgas species fed to a plurality of vacuum chambers 726, 748, and 764 forprocessing semiconductor devices within a single large apparatus oftenreferred to as a “tool.” A group (“pallet”) of mass flow controllers(720, 732, 742, 754, 758, and 776) allow the simultaneous combination ofseveral different gases into a single manifold (742, 744, and 760) whichfeeds a gas distribution structure (“showerhead”) inside a vacuumchamber (726, 748 and 764). Insufficient conductance in the manifoldplumbing may result in the downstream pressure, of a particular group ofmass flow controllers, becoming too high to maintain choked flowconditions within one or more mass flow controllers within the group.The pressure within the manifold may be monitored using pressure sensor724, pressure sensor 746 and pressure sensor 762 and a correspondingsignal provided to all mass flow controllers within the group as analternative to each mass flow controller having a separate thirdpressure sensor. Individual mass flow controller self-correction maythen proceed based upon the shared third pressure sensor signal oraccording to commands emanating from the tool master control (a controlsystem external to the control module of each mass flow controller).

FIG. 7 illustrates an apparatus 700 that includes various systemincluding, a gas provider 702 and a gas provider 704. The apparatus 700has a plurality of valves, 706, 708, 710, 712, 718, 730, 740, 752, 756,and 774. The apparatus 700 includes one or more pressure sensors todetermine the flow rate of the gases. The pressure sensors 714, 716,724, 746, 762, 770, and 772 may be used to determine the pressureoutside of the MFCs 720, 732, 742, 754, 758, and 776.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the scope of theinvention. Accordingly, the foregoing description and drawings are byway of example only.

The invention claimed is:
 1. A mass flow control apparatus comprising: acontrol module configured to receive one or more set point flow ratesfor delivering a fluid delivery to a tool; a variable control valveconfigured to constrict sufficiently to increase a pressure of a fluidfrom a flow restrictor to be higher than a back pressure from the toolresponsive to the control module receiving a second set point flow ratethat is different than a first set point flow rate; and a proportionalcontrol valve located upstream from the flow restrictor to adjust thepressure to the flow restrictor.
 2. The mass flow control apparatus ofclaim 1, wherein the variable control valve is a solenoid-type valve. 3.The mass flow control apparatus of claim 1, wherein the proportionalcontrol valve is a solenoid-type valve.
 4. The mass flow controlapparatus of claim 1, wherein the proportional control valve isconfigured to adjust the pressure to the flow restrictor such that thepressure drop across the flow restrictor yields a flow rate that isequal to the second set point flow rate.
 5. The mass flow controlapparatus of claim 1, further comprising a reference volume configuredto verify an actual flow rate by closing a fluid flow using a shut-offvalve and measuring a pressure rate of decay in the reference volume;wherein at least one of the variable control valve and the proportionalcontrol valve is configured to be adjusted until the second set pointflow rate is achieved.
 6. The mass flow control apparatus of claim 1,further comprising a thermal-based flow sensor.
 7. The mass flow controlapparatus of claim 6, wherein the thermal-based flow sensor includes afluid conduit with two spaced apart temperature responsive elementsaffixed to an exterior of the fluid conduit.
 8. The mass flow controlapparatus of claim 1, wherein the mass flow control apparatus isconfigured to perform a supervision function.
 9. The mass flow controlapparatus of claim 1, wherein the variable control valve can be adjustedto any of at least two different amounts of openings.
 10. The mass flowcontrol apparatus of claim 1, wherein the variable control valve can becontinuously adjusted to a range of openings.
 11. The mass flow controlapparatus of claim 1, wherein the variable control valve can be adjustedto provide a complete shut-off position.
 12. The mass flow controlapparatus of claim 1, further comprising a first pressure sensor, afirst temperature sensor and a shut-off valve, wherein: the firstpressure sensor is configured to measure a fluid pressure (P0) of areference volume downstream from the shut-off valve; the firsttemperature sensor is configured to measure a temperature (T0) of thereference volume; the proportional control valve provides provisions formeasuring a second temperature (T1) and a second pressure (P1) of thefluid contained within a fluid pathway upstream of the flow restrictor;and the flow restrictor provides a provision for measuring a thirdpressure (P2) of the fluid contained within the fluid pathway downstreamof the flow restrictor.
 13. The mass flow control apparatus of claim 1,wherein the flow restrictor is chosen from a group consisting of anorifice, a nozzle, a porous sintered metal element, and laminar flowstructures and tubes.
 14. A mass flow control apparatus comprising: acontrol module configured to receive one or more set point flow ratesfor delivering a fluid delivery to a tool; a variable control valveconfigured to constrict sufficiently to increase a pressure of a fluidfrom a flow restrictor to be higher than a back pressure from the toolresponsive to the control module receiving a second set point flow ratethat is different than a first set point flow rate; a proportionalcontrol valve located upstream from the flow restrictor to adjust thepressure to the flow restrictor; and a pressure sensor for measuringpressure of a fluid.
 15. The mass flow control apparatus of claim 14,wherein the pressure sensor is located upstream of the variable controlvalve.
 16. The mass flow control apparatus of claim 14, wherein thepressure sensor is configured to measure a pressure in a referencevolume portion.
 17. The mass flow control apparatus of claim 14, whereinthe pressure sensor is configured to measure a pressure of the fluidwhen at least one of a shut-off valve and the variable control valve isclosed.
 18. A mass flow control apparatus comprising: a control moduleconfigured to receive one or more set point flow rates for delivering afluid delivery to a tool; a variable control valve configured toconstrict sufficiently to increase a pressure of a fluid from a flowrestrictor to be higher than a back pressure from the tool responsive tothe control module that is configured to receive a second set point flowrate that is different than a first set point flow rate; a proportionalcontrol valve located upstream from the flow restrictor to adjust thepressure to the flow restrictor; a pressure sensor located upstream ofthe variable control valve to measure a pressure of a fluid; and ashut-off valve to close an inlet supply, wherein the pressure sensor isconfigured to measure the pressure of the fluid while the shut-off valveis closed.
 19. The mass flow control apparatus of claim 18, furthercomprising a temperature sensor to measure a temperature of a fluid. 20.The mass flow control apparatus of claim 18, wherein the control moduleis configured to enable additional self-calibration processes, change asystem parameter, and store results.